conferring data to an emitted particle...

["B Miller" <bmillerxsilist(at)gmail.com>]

Hi all,

Particle questions for y'all. I should note in advance that I'm coming from the Maya school and I may be approaching the problem from the wrong angle...

I have a particle system with two Ptypes: and emitter type that zips around in space and a trail type that is emitted in its wake. I'm emitting the trail using an "every N frames" particle event. My problem has to do with getting data contained in the emitter to the trail particle on emission.

The first specific problem is a workaround for staccato emissions with a fast emitter particle, given the fact that we don't have subframe particle emission in XSI. My approach is to emit the particle at a random point along the segment terminated by the emitter's current position and it's previous position, 
i.e. pos - (velocity/fps). To do it right, of course, you factor in the acceleration of the emitter as well. I've used this hack for years in Maya and it works great. Because I can't pass data from the emitter to the trail, however, it's a little confusing how you'd get something like this happen. I ended up making the particle inherit 100% velocity from the emitter. In an "every N particles" event on the trail particle, I pick up the velocity, invert and scale it, pick up the position, add the scaled velocity to the position, then set the velocity to zero. It works, sort of. For some reason, the velocity inherited by each trail particle is scaled somewhere between 0% and 100% of  the emitter's, even through variance is 0 (?!) Dunno how to get around that one, but whatever, since I was going to apply the random variation in the init script anyway.. The trail doesn't join up correctly though, unless you factor in the emitter's acceleration. Is there any hope of making the emitter's acceleration available to the trail particle?

The second specific problem, which is related: I want the size of the emitted trail particle to be based on the emitter particles age%. As the emitter approaches the end of it's life, the emitted trail particles should be smaller. Anybody know of a good way to make this happen?

Thanks for any help at all. If there's a general approach I should be thinking of for getting the particles to submit to my will other than the Maya paradigm, I'd be delighted to hear it.

thank you,

Brett